Morphology-specific hybridization probes were used to screen a cDNA library from Candida albicans in the process of forming hyphae, in order to identify genes that are differentially expressed during morphogenesis. At least 21 different genes, differentially expressed during the dimorphic transition, were identified and cloned. Using transformation techniques we will focus our continuing studies on the mechanisms for controlling gene expression during the dimorphic response. The specific aims are to study the role of these genes in dimorphism by genetic manipulation of their expression, constructing null alleles and inappropriately expressed alleles, and to study the regulation of their expression by in vivo and in vitro promoter analysis. Studies on yeast-hyphal dimorphism in Candida albicans are made compelling by the wide range of pathogenic fungi that exhibit the phenomenon and the possible role that hyphal forms play in the pathogenesis of Candida albicans. Our experiments on the control of transcription of differentially expressed genes are aimed at understanding dimorphism, rather than transcription per se, and employ a range of molecular genetic techniques now available. Knowledge of the mechanisms responsible for the differential expression of gene will be a significant step in our understanding of how Candida albicans responds to its environment and regulates the dimorphic response.